Ensuring that aggregators are properly incentivized is essential for the success and security of the rollup.
Aggregators are responsible for collecting and bundling transactions from users into a single rollup block. They execute these transactions off-chain and generate a new state root that represents the updated state of the rollup. The aggregators then submit the new state root, along with a cryptographic commitment of the bundled transactions, to the Ethereum main chain.
To ensure that aggregators act honestly and efficiently, Optimistic Rollups rely on a combination of economic incentives and technical mechanisms. These incentives are designed to encourage aggregators to submit valid state transitions and discourage them from attempting to submit fraudulent ones.
The primary source of revenue for aggregators comes from transaction fees. Users who wish to have their transactions included in a rollup block must pay a fee to the aggregator. These fees are typically lower than the fees required for on-chain transactions, making Optimistic Rollups an attractive option for users looking to save on transaction costs.
In some implementations of Optimistic Rollups, aggregators may also receive block subsidies. These subsidies, which are generated through inflation or other mechanisms, serve as an additional source of revenue for aggregators and help to ensure that they are adequately compensated for their work.
The process of selecting aggregators can have a significant impact on the security and efficiency of an Optimistic Rollup. There are several methods that can be used to choose aggregators, each with its own trade-offs:
In a PoS-based aggregator selection model, aggregators must stake a certain amount of tokens to participate in the system. The likelihood of being selected to propose a rollup block is proportional to the amount of tokens staked. This model incentivizes aggregators to act honestly, as they risk losing their staked tokens if they are caught submitting invalid state transitions.
A PoW-based model requires aggregators to solve cryptographic puzzles in order to propose rollup blocks. This model can provide a degree of decentralization, as it allows any participant with sufficient computational resources to become an aggregator. However, the energy consumption and hardware requirements associated with PoW can be significant drawbacks.
In an auction-based model, aggregators compete for the right to propose rollup blocks by bidding on them. The highest bidder wins the right to propose the next block and collects the associated transaction fees. This model can promote competition among aggregators and encourage efficiency, but it may also lead to centralization if a small number of well-funded participants consistently win the auctions.
To discourage aggregators from submitting invalid state transitions, Optimistic Rollups impose penalties on those who are caught submitting fraudulent data. These penalties can take several forms: